1. Field of the Invention
The present invention generally relates to a magnetic transducer head utilizing magnetoresistance effect and more particularly is directed to a multichannel magnetic transducer head utilizing magnetoresistance effect.
2. Description of the Prior Art
An example of a conventional magnetoresistance effect (hereinafter simply referred to MR) type magnetic reproducing transducer head, particularly a rear type magnetic transducer head in which the MR element thereof is placed at the position backward from the contact surface of the head with a magnetic recording medium is shown in, for example, FIGS. 1 and 2. FIG. 1 is a schematically enlarged plan view of a main part thereof and FIG. 2 is a schematically enlarged cross-sectional view taken along a line A--A in FIG. 1. As shown in FIGS. 1 and 2, on an insulating magnetic substrate 1 made of, for example, ferrite containing Ni - Zn is deposited a band shaped conductor film 2 which constitutes a current path as a bias magnetic field generating means for applying a bias magnetic field to the MR element by electromagnetic induction or the like. On the band shaped conductor film 2 is deposited a thin film MR effect element 4 made of, for example, alloy containing Ni - Fe or Ni - Co or the like through an insulating layer 3. Further, on the MR effect element 4 are deposited a pair of magnetic layers 6 and 7 made of alloy containing Ni - Fe or the like through an insulating layer 5. In this case, the magnetic layers 6 and 7 are located in the direction across the MR effect element 4 and opposed face to face on the MR effect element 4 so as to hold a predetermined spacing G therebetween. The outer end portion of magnetic layer 6 is opposed through at least one of the insulating layers 3 and 5 to the substrate 1, thus forming a magnetic gap g, while the outer end portion of the magnetic layer 7 is contacted with the substrate 1 through windows formed through the insulating layers 3 and 5. The conductor layer 2, the MR effect element 4 and the magnetic layers 6 and 7 are coated with a non-magnetic protective layer 8 on which a protective substrate 10 is bonded by use of an adhesive layer 9. And, over both the substrates 1 and 10 is formed a contact surface 11 with a magnetic recording medium and the magnetic gap g faces on this contact surface 11. The magnetic path which includes the magnetic gap g and the MR effect element 4, namely, the magnetic path of the magnetic substrate 1 - the magnetic gap g - the magnetic layer 6 - the MR effect element 4 - the magnetic layer 7 - the magnetic substrate 1 is formed.
With the configuration thus made, when a predetermined bias magnetic field generated by flowing current I.sub.B through the conductor layer 2 is applied to the MR effect element 4 and a current I is flowed through the MR effect element 4, an electrical signal, namely, output signal due to the resistance change in the MR effect element 4 caused by applying a magnetic flux from a recorded magnetic signal of the magnetic recording medium which is contacted with or opposed to the magnetic gap g is derived from both ends of the MR effect element 4.
However, such MR effect type magnetic transducer head, particularly the rear type magnetic transducer head in which the magnetic material members are mounted close to the MR effect element has such a problem that its magnetoresistance characteristic is nonlinear. Namely, in the magnetic transducer head of this kind, magnetic field H versus resistance R characteristic of the MR effect element 4 indicates a parabola as shown in FIG. 3. Accordingly, if, as shown in FIG. 3, the magnetic signal as indicated by reference numeral 12 is applied to the MR effect element 4 under the state that the bias magnetic field H.sub.B is applied to this MR effect element 4, the output signal provided by the resistance change in the MR effect element 4 becomes asymmetrical and distorted signal as shown by reference numeral 13. In this connection, the magnetoresistance characteristic when the magnetic material members are not close to the MR effect element has the extended skirt portion as shown in FIG. 4. Since the characteristic partially includes a portion having superior linearity, under a predetermined bias magnetic field H.sub.B ', it is possible to obtain an output signal 13' which has no distortion and superior symmetry against a magnetic signal 12'. This is because of the influence of demagnetizing field generated at both sides of the MR effect element. While the magnetic transducer head such as rear type configuration as shown in FIGS. 1 and 2 in which the magnetic layers 6 and 7 are placed close to both side end faces of the MR effect element 4, the influence of such demagnetizing field upon the magnetoresistance characteristic is small.
As can also be seen from FIG. 3, when operating to the right of the vertical axis (+H.sub.B), addition of a further positive magnetic field or a positive increase in H.sub.B moves the operating point on the curve to the right, thus causing a decrease in resistance. When operating to the left of the vertical axis (-H.sub.B), the same further positive magnetic field or positive increase in -H.sub.B still moves the operating point to the right, but causes an increase in resistance.
As a magnetic transducer head utilizing magnetoresistance effect which can remove the nonlinear component of the magnetoresistance characteristic in the MR effect element, there is proposed such one in which MR effect elements are constituted in a differential type configuration.
As shown in FIG. 5, the differential type MR magnetic transducer head comprises two MR effect elements MR.sub.1 and MR.sub.2 of which respective ends opposite to each other are connected to common terminal t.sub.3 and other respective ends are led out to terminals t.sub.1 and t.sub.2. Terminals t.sub.1 and t.sub.2 are respectively connected to independent constant current sources S.sub.1 and S.sub.2 and also connected to input terminals of a differential amplifier Amp. A common terminal t.sub.3 is supplied with a predetermined potential, for example, a ground potential. The MR effect elements MR.sub.1 and MR.sub.2 are respectively supplied with constant currents i in the direction opposite to each other, and also supplied with bias magnetic fields H.sub.B which are in the direction perpendicular to the constant currents i and opposite to each other. According to the differential type magnetic transducer head with this construction, when the MR effect elements MR.sub.1 and MR.sub.2 are commonly supplied with an input signal of magnetic flux from a magnetic recording medium, output signals 14.sub. 1 and 14.sub.2 having an opposite polarity as shown in FIG. 6 are derived from the MR effect elements MR.sub.1 and MR.sub.2 to the amplifier Amp so that from the output terminal t.sub.out of the differential amplifier Amp appears a signal 14 having a positive and negative symmetry provided by composing these signals, namely, the nonlinear components being cancelled out.
In accordance with the differential type MR magnetic transducer head of such constant current type, the nonlinear components of the magnetoresistance characteristic of the MR effect elements MR.sub.1 and MR.sub.2 can be cancelled out. Hence it is possible to obtain a reproduced signal excellent in symmetry and with no distortion. The magnetic transducer head of this kind, however, requires three terminals t.sub.1 to t.sub.3 to be led out, two independent signal lines connected to the diffrential amplifier Amp and two independent constant current sources S.sub.1 and S.sub.2. Therefore, when this magnetic transducer head is applied to the multichannel magnetic transducer head, if the number of channels is taken as n (n is a positive integer), this multichannel magnetic transducer head requires at least 2n+1 (in number) terminals and further requires at least 2n (in number) constant current sources. Moreover, because of the constant current driving, the above multichannel magnetic transducer head consumes large power and the circuit thereof becomes large. Thus, the above differential type magnetic transducer head is not suitable for the multichannel magnetic transducer head having, for example, n selected in a range from 10 to 50.
To remove such defects, there is proposed a magnetic transducer head in which a pair of MR elements are coupled in series, a constant voltage is applied across both outer ends thereof and an output is differentially derived from the connected point between both the elements.
According to the differential type magnetic transducer head of such constant voltage driving system, in the same way as in the afore-mentioned constant current driving system, it is possible to cancel out the second-order harmonic components. The sensitivity under the same power consumption is reduced to the half that of the constant current driving system, however, S/N (signal-to-noise) ratio and signal power under the same power consumption are equal to those of the constant current driving system. And, as compared with the differential type MR magnetic transducer head of the constant current type, it is not necessary to provide two independent constant current sources for each channel and to lead out a large number of terminals and their wirings. Thus, there is a great advantage for the multichannel type magnetic transducer head that the configuration thereof can be simplified.
As such MR magnetic transducer head of the constant voltage driving type, there is proposed MR magnetic transducer head of the self-biasing type. The MR magnetic transducer head of the self-biasing type configuration is disclosed in the public unexamined Japan patent application No. 23920/1977 or proposed as so-called barber pole type. In these magnetic transducer heads, the direction of the current path through each MR element has a predetermined angle against the direction of easy magnetization of each element so that the current flowing through the element allows the bias magnetic field having a predetermined angle against the current path to occur. In the MR magnetic transducer head of, for example, barber pole type, with the inclination relative to the direction of easy magnetization along the longitudinal direction of the thin film MR element, namely, just like the obliquie patterns in the barber pole, a plurality of good conductive band lines made of, for example, Au are placed in parallel to hold a predetermined spacing therebetween. In this case, if the MR element of the multichannel magnetic transducer head is reduced in size in order to reduce the width of the channel pitch, it is necessary to reduce the spacing between the conductor band lines. In association therewith, the substantial resistance of the MR element becomes small, resulting in various problems such as difficult handling of the output signal.
Furthermore, in the thin film magnetic transducer head of this kind as shown in FIGS. 1 and 2, when a human body, for example, a hand touches the terminal of the magnetic transducer head or the magnetic layer or core 6 which faces to the contact surface 11 with the magnetic recording medium, the discharge of static electricity accumulated in the human body or the induced voltage destroys each of the insulating layers 3 or 5 between the MR element 4 and the bias conductor member 2, between the magnetic cores 6, 7 and the MR element 4, and further between the bias conductor member 2 and the magnetic cores 6, 7 and the breaking of wires is caused in each portion of the thin film MR element and the like thus producing no good products or troubles.